There are very few locks in life, yet when Chien-Ming Wang is on the hill for the Yankees, wagering on the Bombers is a wise investment. Even on nights when his back barks and he is removed from the game.

That’s what happened last night at Yankee Stadium where Wang was brilliant, his back stiffened and the Yankees’ bats woke up. Wang and the hot wood parlay resulted in a 12-3 spanking of the Mariners in front of 52,487 fans.

Wang allowing one run and five hits in 71/3 innings was comforting, him leaving in the eighth after getting the first out was disturbing. Especially since the Yankees are terrible in games not started by Andy Pettitte and Wang.

“I am not worried,” Wang said of the lower back stiffness that forced him from his 17th win, which tied Josh Beckett for the most victories in the majors.

Joe Torre said Wang’s back stiffened while he sat in the dugout watching the Yankees score seven runs in the seventh. Torre said since Wang had thrown 84 pitches and isn’t slated to pitch until next Tuesday due to off days, the decision was made to send him out for the eighth.

Because Wang wasn’t instructed to arrive early today for extra treatment, the problem appears over. However, any time a Cy Young candidate exits in September with his team fighting for a spot in October, it raises red flags.

So, too, does the sight of Alex Rodriguez on the ground holding his right leg like he did in the seven-run seventh after sliding into the base.

“I knew it was going to take me a long time to get to third base and I didn’t want bad news when I got there,” Torre said.

Rodriguez stayed in the game, scored a run then was hit for by Albert Gonzalez when the Yankees batted around. X-rays of the ankle were negative. Rodriguez said he needed to see how he felt this morning before knowing if he will play tonight.

Wang has won four straight and seven of his last eight decisions. In the last 10 games started by Pettitte and Wang, the Yankees are 9-1. In 13 games worked by other starters the Yankees are 3-10. Proof that his trademark sinker was working, 17 of the 22 outs Wang registered were on the ground.

Wang was backed by a 20-hit attack that was led by Jorge Posada’s four hits and two homers. Rodriguez and Bobby Abreu, who went 4-for-5, also homered. Robinson Cano, who was in a 5-for-24 (.208) slump, went 4-for-5 and drove in three runs for the winners who stretched their wild-card lead over the reeling Mariners to two games and 3½ over the Tigers. The Mariners have lost 10 of 11.

“He sat for about 40 minutes,” said pitching coach Ron Guidry, who noticed Wang unable to fully bend on his first two pitches in the eighth. “I could tell he was trying to get his back loose.”

Guidry went to the mound where Posada was already informed that Wang’s back was acting up.

“It didn’t look good,” Posada said. “The two pitches he threw I wanted to make sure he was OK. He said it was just tight and I told the dugout. There is no concern whatsoever. You don’t want him hurt, he is too valuable. That’s why I went out there, but he is fine.”